The invention relates to an arrangement for controlling a variable position of vanes in a flow channel of a turbine. The invention furthermore relates to a turbocharger for an engine including a turbine rotatably mounted on a shaft, a compressor impeller mounted on a shaft, a compressor housing having an inlet and an outlet and enclosing said compressor impeller, a center housing including bearing means for rotatably supporting the turbine shaft and compressor shaft, a turbine housing including an inlet and an outlet, said turbine housing forming a volute therein for directing exhaust gas from said engine through an annular passage to said turbine, and a flange member mounted between said center housing and said turbine housing, which turbocharger further includes an arrangement for controlling a variable position of vanes at a turbine inlet.
The invention also relates to an engine including a turbocharger unit.
Supercharged diesel internal combustion engines used in commercial vehicles are frequently equipped with turbochargers with variable inlet geometry such to adjustably set the effective turbine cross section. This is accomplished by adjusting the angular position of a set of vanes being arranged in an annular passageway in the turbine housing. The annular passageway is connecting the scroll shaped volute defined in a turbine housing to a turbine chamber where a turbine is located. Each vane is connected to a vane pin housed in a nozzle ring. The vane pin is connected to a vane arm which connects the vane pin with a unison ring. Pivotal movement of the unison ring enables simultaneous pivoting of the vanes in the annular passageway. The unison ring is pivotally arranged in a trace formed in the turbine housing or a flange member attached to the turbine housing. In order to accomplish the pivoting movement of the unison ring an unison ring displacement arrangement is provided. The unison ring displacement member includes a pivot axle housed in said flange member, a first actuator arm arranged on said pivot axle, which first actuator arm is connectable to a drive actuator, a second actuator arm arranged on said pivot axle, which second arm is connected to a pin engaged with the unison ring. Using an actuator to act on the first actuator arm turns the pivot axle and thereby the second actuator arm connected to the pivot axle. The second actuator arm, being connected to the unison ring via the pin enables pivoting of the unison ring around its rotational axis. In order to control the end positions of the vanes, in particular when the vanes are set to delimit a narrow gap in between the tips of the vanes, a stop screw is used. According to prior art the stop screw delimits the movement of the first actuator arm by defining an end stop in one of its positions. Two stop screws may be used variably defining respective end position of the vanes. Since the end position corresponding to a minimum throat area defined by the vanes requires the most precise positioning, it may be sufficient to use a stop screw for this position, while the other position may be defined by the actuator or a fixed end stop.
An example of such an arrangement is presented in U.S. Pat. No. 4,659,295. It is desirable to improve the precision in control of at least one of the maximum or minimum throat area.
According to an aspect of the invention an arrangement for controlling a variable position of vanes in a flow channel of a turbine inlet, which arrangement including a nozzle ring carrying a set of vanes is provided. The vanes are to be mounted in an annular passageway in a turbine housing. The annular passageway is connecting a scroll shaped volute defined in a turbine housing to a turbine chamber where a turbine is located. Each of said vanes being connected to a vane pin housed in the nozzle ring. The rotational position of the vanes is set by rotating the vane pin. This is accomplished via a vane displacement drive train including the following members:                a pivotally supported pivot axle, a first actuator arm arranged on said pivot axle, which first arm is connectable to a drive actuator, a second actuator arm arranged on said pivot axle, which second arm is connected to a pin engaged with an unison ring for pivoting the unison ring, and a vane arm being connected to each vane pin and the unison ring for displacement of said vanes via pivotal displacement of the unison ring. The control of the position of the vane is thus performed by operating a bell crank system connected to a vane pin via a unison ring. The bell crank mechanism is including a pivot axle having a first and second arm. The first arm may be actuated by operation of an actuator. The second arm is connected to a unison ring via a pin. The unison ring is rotatably arranged around a nozzle ring rotatably supporting a set of vane pins. A vane arm is connecting each vane pin with the unison ring for rotation of the vane pin by turning the unison ring.        
A stop screw is arranged for limiting the pivotal displacement of said vanes. According to the invention the stop screw is arranged to limit the displacement of a member in said vane displacement drive train which is located closer to the vane pin in the vane displacement drive train than said pivot axle. The ability to precisely control the position of the vanes are dependent on the precision of the position of the members in the vane displacement drive train. When the stop screw is in contact with a member to define an end position, play between the members, tolerances of the members and the non-infinite rigidity of the members, reduces the precision of the actual position of the vane. For this reason, the stop screw should be arranged to act on a member of the vane displacement drive train which is close to the vane pin.
It has shown that it is advantageous to arrange the stop screw to act on the second actuator arm of the bell crank mechanism. The bell crank mechanism is normally mounted to a flange member extending from the turbine housing, such that the pivot axle extends through the flange member, having the first actuator arm externally accessible for an actuator and the second arm being positioned inside an enclosure formed by a turbine housing and/or a flange member. By allowing the stop screw to act on the second actuator arm, it is possible to arrange a seating for the stop screw in the flange member or in the turbine housing, depending on the actual configuration of the turbine housing and/or the flange member. The turbine housing and the flange member are normally cast members. The position of the seating for the stop screw can thus be manufactured with high requirement on the tolerance at low cost in comparison with the current practice to arrange a mounting bracket on the flange member. Mounting of mounting brackets can normally not be made with a high precision at low cost. Furthermore, the brackets themselves add to the tolerance by their low rigidity and added play.
It is also advantageous to allow the stop screw to act on the unison ring. For this reason the unison ring must be provided with a stop member, which may be formed by a notch or a recess on the ring. The stop member may be positioned on the outer perimeter or on the side of the unison ring. In the event the stop screw acts on the unison ring, the stop screw will be arranged in a seating integrally arranged with the turbine housing.
In an embodiment the stop screw is arranged to limit the displacement of the vane arm. This embodiment the stop screw is located as closely as possible to the vane pin.
In a further embodiment a turbine inlet is defined in a turbine housing. A flange member is attached to said turbine housing, the flange member and/or the turbine housing defining an enclosure in which said unison ring is located. The first actuator arm will located outside the enclosure for access by an actuator mechanism. In order to have access to the stop screw while the stop screw has an end position that defines an end stop for a member in the vane displacement drive train that is located closer to the vane pin than the pivot axle of the bell crank mechanism, which pivot axle also extends through said enclosure, the stop screw extends though said enclosure.
The flange member and/or turbine housing may be formed as cast elements. A seating for the stop screw may integrally formed in one of said cast elements.
The invention also relates to a turbo arrangement including an arrangement for controlling a variable position of vanes as described above and to a combustion engine including a turbo arrangement equipped with an arrangement for controlling a variable position of vanes.